This invention relates to a bipolar cell unit for use in a metal/air battery, in particular in an aluminum/air battery.
Metal/air batteries produce electricity by the electrochemical coupling of a reactive metallic anode to an air cathode through a suitable electrolyte in a cell. As is well known in the art, an air cathode is a typically sheet-like member, having opposite surfaces respectively exposed to the atmosphere and to the aqueous electrolyte of the cell, in which during cell operation atmospheric oxygen dissociates while metal of the anode oxidizes, providing a usable electric current flow through external circuitry connected between the anode and cathode. The air cathode must be permeable to air but substantially hydrophobic so that aqueous electrolyte will not seep or leak through it, and must incorporate an electrically conductive element to which the external circuitry can be connected; for instance, in present-day commercial practice, the air cathode is commonly constituted of active carbon (with or without an added dissociation-promoting catalyst) containing a finely divided hydrophobic polymeric material and incorporating a metal screen as the conductive element. A variety of anode metals have been used or proposed; among them, alloys of aluminum and alloys of magnesium are considered especially advantageous.
An example of a typical metal/air cell is shown in Hamlen et al., U.S. Pat. No. 4,626,482 issued Dec. 2, l986. It typically comprises a tank defining a reservoir for liquid electrolyte. An air cathode is provided having opposed vertical surfaces with means for supporting the cathode for simultaneous exposure of one of its surfaces to air and the other of its surfaces to electrolyte in the reservoir. A metal anode is provided in the form of a metal plate having opposed vertical major surfaces, disposed for immersion in the electrolyte in the reservoir with one plate major surface positioned in spaced juxtaposition to the other of the cathode surfaces to define therewith an anode-cathode gap for receiving the electrolyte, and with the other plate major surface exposed to electrolyte and facing a region of the reservoir external to the gap. Circuit means are provided for connecting the anode and cathode to an external load.
The conventional air cathode is in the form of a rectangular sheetlike member having two opposed planar major surfaces, being constituted, for example, of two flat layers of an active carbon-hydrophobic polymer composition with a wire screen conductor pressed between them. In order to provide strength to the cathode, the sheetlike member must be mounted in a plastic frame with the edges securely sealed to the frame in the form of a continuous liquid-tight joint. This cathode assembly is then mounted in a framework which holds it in spaced relationship with an anode.
Such a structure is expensive and time-consuming to manufacture and is not amenable to mass production. It is the object of the present invention to provide a greatly simplified form of metal/air bipolar cell unit which will be both much less expensive and simpler to manufacture than any of the prior systems.